1. Field of the Invention
The present invention relates to an ignition circuit for a squib (ignition apparatus) which is used in a system which employs an explosive, such as, for example, an air bag device or a pretensioner apparatus for an automobile, and particularly relates to an ignition circuit for a squib which can be ignited with low energy.
Priority is claimed on Japanese Patent Application No. 2004-020972, filed Jan. 29, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
In recent years, a squib is used for the purpose of igniting a gas generating agent in order to operate a system such as, for example, an air bag device or a pretensioner apparatus.
Generally, a squib is attached to an inflator which contains a gas generating agent of the apparatus which employs each explosive.
As a structure of the squib, a heat producing portion is attached to a header which fixes a pin, and an explosive is press-inserted in order to contact with the heat producing portion by a cup.
The pin of the squib is electrically connected with a control unit which is used as a master.
Moreover, as the squib which is mounted to a safety device for an automobile which is increasing in recent years, a low energy squib which operates with slight electric power is proposed.
This kind of low energy squib has the heat producing portion which includes an electrically conductive portion and a fuel portion, and has a structure which efficiently produces heat as compared with an ordinary squib (Patent Document 1: U.S. Pat. No. 5,847,309, Patent Document 2: U.S. Pat. No. 5,905,226, and Patent Document 3: U.S. Pat. No. 6,192,802).
When electrical current is supplied to the heat generation portion, an excited chemical reaction occurs, and a great amount of heat is generated.
In order to operate the low energy squib which is constituted in such a manner, first of all, when the collision of a car is detected with the signal from a sensor by the control unit, the control unit supplies electrical current from an ignition circuit to each squib which is attached thereto in order to operate each safety device (several A (amperes)×several millisec).
The heat producing portion is heated by this supplied electrical current, and thereby explosive which is adjacent to the heat producing portion is ignited.
Furthermore, each safety device is operated by making a gas generating agent ignited in the inflator with heat and pressure of an explosive which was ignited.
However, conventionally, since electrical current was supplied for a long time (on the order of milliseconds) for the low energy squib as well as the ordinary squib, a large quantity of heat was diffused from the heat producing portion to the outside because a supplying time of electrical current is long, and it was difficult for heat to be efficiently transmitted to the heat producing portion.
Therefore, in order to operate the low energy squib, surplus energy was needed, thereby there was a problem in that an obstacle for further reduction in energy arose.